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4430-V & VN BPSK/QPSK VME Demodulator & Optional Modulator User’s Manual
Doc: 4430_V,VN.fm, © 11 Jul 2005, 14:55
To program this register, follow the procedure below.
1.
Determine the filter range by evaluating the following:
Mod LP Filter Range (f
LM
) = Mod f
c
+ (2 x Symbol Rate)
2.
Using the results of Step 1, select the coefficients K
0
, K
1
, K
2
, and K
3
from the
table below:
Table 3.5.30: Modulator Low Pass Filter Turning Ranges
3.
Using the coefficients selected in Step 2, evaluate the following equation:
Mod LP Filter = (K
0
x f
LM
3
) + (K
1
x f
LM
2
) + (K
2
x f
LM
) + K
3
4.
Round the value from Step 3 and limit it to the range of 0 to 255.
5.
Convert the number to a hexadecimal value and write the value to register
3Ah.
Programming
Example
For the programming example given, the following steps apply:
1.
Determine the filter range by evaluating the following:
Mod LP Filter Range (f
LM
) = Mod f
c
+ (2 x Symbol Rate)
Mod LP Filter Range (f
LM
) = 8000 + (2 x 1000) = 10000Hz
2.
Using the results of Step 1, select the coefficients K
0
, K
1
, K
2
, and K
3
from
Table
3.5.30
:
K
0
= 0
K
1
= -1.89 x 10
-8
K
2
= 1.48 x 10
-2
K
3
= -20
3.
Using the coefficients selected in Step 2, evaluate the following equation:
Mod LP Filter = (K
0
x f
LM
3
) + (K
1
x f
LM
2
) + (K
2
x f
LM
) + K
3
Mod LP Filter = (0) + (-1.89) + (148) - 20 = 126.11
4.
Rounding the value from Step 3 and limiting it to the range of 0 to 255:
Mod LP Filter = 126
5.
Converting the number to a hexadecimal value results in a value of 7Eh being
written to register 3Ah.
Modulator LP Filter Range
Step
K
0
K
1
K
2
K
3
175 kHZ
≤
f
LM
≤
7.5MHz
00b
1.51
x
10
-18
-2.57
x
10
-11
1.37
x
10
-4
-10.65
17kHZ
≤
f
LM
< 175kHz
01b
0
-2.65
x
10
-12
1.34
x
10
-8
-12.56
4kHz
≤
f
LM
< 17kHz
11b
0
-1.89
x
10
-8
1.48
x
10
-2
-20
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